Multipoint contacts employing the arc rotating principle



Sept. 27, 1966 H. M. PFLANZ ET AL 3,275,777

MULTIPOINT CONTACTS EMPLOYING THE ARC ROTATING PRINCIPLE Filed Nov. 25, 1964 United States Patent 3,275,777 MULTIPOINT CONTACTS EMPLOYING THE ARC ROTATING PRINCIPLE Herbert M. Pflanz, Nuenen, Netherlands, and Zygmunt A. Wachta, Boston, Mass, assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Nov. 25, 1964, Ser. No. 413,820 Claims. (Cl. 200-144) This invention relates generally to contacts for electric circuit breakers. More particularly, it relates to multipoint contacts employing the arc rotating principle for use in circuit breakers such as vacuum type breakers.

In electric circuit breakers circuit interruption is accomplished by separating a pair of relatively movable contacts to establish an arc therebetween. Interrupting capacity of the contacts can be increased by rotating or otherwise moving the arc terminals at high speed across the contact surfaces. In one known type of arrangement, at least one of the contacts is disk shaped and is provided with one or more spiral slots which extend from its outer periphery inwardly to provide a magnetic effect that continuously drives the are about the periphery of the disk in one direction until it is extinguished. However, in the foregoing type of arrangement when the contacts are closed there is only a single point, line or surface at which the contacts mate. Because of contact welding, single point contacts are in general limited to momentary currents below 15,000 amps. Thus, in order to construct high momentary current contacts the principle of multipoint contacts must be employed, so that each contact carries only a fraction of the total current. In vacuum switches multiple arclets in parallel have been observed to exist simultaneously and a multipoint contact as disclosed herein facilitates formation of multiple arclets upon separation of the contacts which aids instability during interruption.

It is an object of the present invention to provide contacts which combine the advantages of multipoint contacts and the advantages of arc rotating contacts.

Another object is to provide contacts of the aforesaid character which are relatively easy to fabricate, selfcleaning and reliable in use.

Other objects and advantages of the invention will hereinafter appear.

A contact constructed in accordance with the present invention comprises a plurality of electrically conductive rods. Each rod comprises a straight shank portion, a first curved portion connected to the shank and curving back upon itself, and a second curved portion connected to the first curved portion and curving off to one side. The straight shank portions of the plurality of rods comprising each contact structure are held parallel to each other by suitable'means such as by being disposed in a holder. When a pair of contacts constructed as above described are in engagement with each other, each rod in one contact makes point contact with one or more opposing rods in the other contact. As the pair of contacts separate, an arc is initiated and is driven by means of an electromagnetic force along the opposing contact rods in a manner similar to the movement of an are along closely spaced parallel runners. As the arc reaches the end of one set of opposing contact rods, it transfers to the next set of opposing rods and continues around until a current zero condition is reached to cause arc extinction.

The accompanying drawing illustrates two preferred embodiments of the invention but it is to be understood that the embodiments illustrated are susceptible of modification with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a cross sectional view of a vacuum interrupter 3,275,777 Patented Sept. 27, 1966 employing one embodiment of a pair of contacts incorporating the present invention;

FIG. 2 is an enlarged cross sectional view of the pair of contacts shown in FIG. 1 with portions thereof omitted for purposes of illustration;

FIG. 3 is an end view of the pair of contacts taken along line IIIIII of FIG. 2; and

FIG. 4 is a view of a pair of contacts similar to those in FIGS. 1, 2 and 3 but arranged with respect to each other to provide another embodiment of the invention.

Referring to FIG. 1, the numeral 10 designates a vacuum type electric circuit interrupter or switch employing contacts incorporating the present invention. It is to be understood, however, that contacts incorporating the pres ent invention can be employed in other types of circuit breakers.

Vacuum switch 10 comprises a cylindrical envelope 12 which may be formed, for example, of a suitable vitreous material. One end of envelope 12 is provided with an annular rim 14 to which is rigidly secured in a vacuum tight connection thereto one end of a ring or flange 16. A metallic cap 18 is sealed along its edge to the other end of flange 16. Cap 18 supports a stationary contact support 20 which extends along the longitudinal axis of envelope 12 and is rigidly supported so as to be restricted against longitudinal or lateral movement. The opposite end of envelope 12 is provided with an annular rim 22 to which is rigidly secured in a vacuum tight connection one end of a ring on flange 24. A tube or retainer 26 is sealed along its rim in a vacuum tight connection to flange 24. A metallic cylindrically shaped flexible bellows 28 is rigidly secured in a vacuum tight connection at one end thereof to retainer 26. The other end of bellows 28 surrounds and is rigidly secured in a vacuum tight connection to a movable contact support 30 which is arranged to extend through retainer 26 into envelope 12 and is in cooperating relationship with contact support 20.

The relatively movable contact supports 20 and 30 may be made of a suitable electrically conductive material such as copper or the like. Contact support 30 is understood to be arranged for longitudinal movement along its axis for a limited predetermined distance by a suitable contact actuating mechanism (not shown).

The contact supports 20 and 30 support contacts 32 and 34, respectively, hereinafter described. In order to control the dispersion of arcing products emitted upon separation of the contacts 32 and 34, a cylindrical cup shaped tube or shield 36 is provided which is rigidly secured to contact support 20 and is arranged to extend beyond the adjacent ends of both contact supports 20 and 30 so as to surround the contacts 32 and 34 when the contacts are engaged and disengaged. Shield 36 may be formed of glass or any suitable metallic or nonmetallic material.

Upon actuation of movable contact support 30 in axial contact engaging or contact disengaging direction, bellows 28 deflects, allowing restricted longitudinal movement of contact 34. The required range of movement of contact 34 is very small. For example, with only 7 of an inch separation between engaging surfaces of contacts 32 and 34 a current of several thousand amperes at an AC. voltage of 18,000 can be safely interrupted. The contacts when engaged can continuously conduct current of several hundred amperes and can carry a momentary current of several tens of thousand amperes without contact welding.

FIG. 2 shows that contact structure 32 comprises a plurality of electrically conductive rods 40, 42 and 44. In the embodiment shown three contact rods are employed but more or less could be utilized if desired. As FIG. 3 shows, the rods 40, 42, and 44 are identical to each other in configuration therefore only rod 40 will be described in detail. Rod 40 comprises a straight shank portion 40a, a first curved portion 40b connected to portion 40a and curving back upon itself, and a second curved portion 400 connected to portion 40b and curving oif to one side. More specifically, shank portion 40a of rod 40 lies in a first plane. Curved portion 40b of rod 40 is curved back upon itself in the first plane to a second plane which is normal to and intersecting with shank portion 40a. Curved portion 400 of rod 40 lies in a third plane which is parallel to and spaced apart from the second plane. Cum ed portion 400 of rod 40 is shown as having the shape of a portion of the perimeter of a circle but it could have some other configuration. Curved portion 40c of rod 4% curves to the right with respect to FIG. 3.

The axes of the shank portions 40a, 42a and 44a of the rods 40, 42 and 44, respectively, lie parallel to and spaced from a line 49 (shown in FIG. 2) on which point 50 (shown in FIG. 3) lies. Each of the rods 40, 42 and 44 is spaced an angular distance of 120 from its adjacent rods so that the rods are arranged in regular order around line 49.

Means are provided to hold the rods 40, 42 and 44 of contact 32 in proper relationship with respect to each other and to adapt them for mounting on contact support 2t) of vacuum switch 10. Such means takes the form of an electrically conductive holder 52 which is provided with a threaded opening 54 for accommodating the threaded end of contact support 20. Preferably, holder 52 is provided with a set screw 56 for locking it in position on contact support 20. Holder 52 is further pro-- vided with a plurality of holes 58, each of which accommodates a single contact rod which is brazed, welded or otherwise secured therein. Preferably, the curved portions 40c, 42c and 440 of rods 40, 42 and 44, respectively, should be located relatively close to holder 52 so that during operation any deflection of the rods during contact closing is limited as the rods come to rest against the holder. This mode of support makes the contact more rigid, especially if the rods are formed of relatively resilient material such as beryllium copper alloy.

As will be understood, contact 34 is similar to contact 32 hereinbefore described in construction and comprises vcontact rods 60, 62 and 64 and a holder 66. However, as FIGS. 2 and 3 show, during fabrication the curved portions 60c, 62c and 64c of the rods 60, 62 and 64, respectively, are curved in a reverse direction as compared to those in contact 32 so that when disposed opposite to each other the curved portions in both sets of contact rods are curved in the same direction. As FIGS. 1, 2 and 3 show, the rods 60, 62 and 64 of contact 34 are arranged in regular angular order around line 49 shown in FIG. 2. However, contact 34 is rotated with respect to contact 32 so that upon contact engagement each rod in one contact makes point contact with two adjacent rods in the other contact as FIG. 3 shows.

FIG. 4 shows another embodiment of the invention wherein the contacts 32 and 34 are arranged or rotated with respect to each other so that the contact rods in one contact are aligned with those of the other. In his arrangement, when the contacts are engaged, each rod in one contact makes point contact with only one corresponding rod in the other contact.

The embodiment of the invention shown in FIGS. 1, 2 and 3 operates in the following manner. Assume first that the contacts 32 and 34 of vacuum switch are in the open position as shown. Upon axial movement of movable contact support to the left (with respect to FIGS. 1 and 2), the contacts 32 and 34 are understood to move into engagement with each other in such a mannor that each rod in one contact makes point contact with two other rods in the other contact. Each contact point is spaced radially outward from center line 49 (FIG. 2) on which point (FIG. 3) lies. Upon separation of the contacts 32 and 34 with electric current flowing there- 4 through an electric arc can be initiated for every contact point. Each arc has one of its arc terminals located on the contact point of a rod in contact 32 and the other arc terminal on the corresponding contact point of a rod in contact 34. Upon initiation of an arc, each are terminal is located at a point spaced radially outwardly from center line 49. Thus, for example, current flows in a looped path through shank portion 40a and through first curved portion 40b of contact rod 40'of contact 32, through an arc path, and then through first curved portion 60]) and through shank portion 60a of oppositely disposed contact rod 60 in contact 34.

Current fiow through such a looped path, as is well known, provides an electromagnetic force which drives the arc outwardly along the opposing contact rods 40 and 60 in a manner similar to the movement of an are along closely spaced parallel arc runners. As the arc reaches the ends of the contact rods 40 and 60, it transfers to the next set of contact rods 44 and 64. The arc continues to rotate around the periphery of the contacts 32 and 34 in the manner described until a current zero condition is reached and it becomes extinguished.

The embodiment of the invention shown in FIG. 4 operates in a manner similar to the embodiment hereinbefore described, except that since the contacts 32 and 34 in FIG. 4 are aligned, the contact point can be chosen by design anywhere along the circular portion of the arc runners as on the highest point of curved section 40!). Accordingly, the loop formed by the opposing curved contact rods and the initial are upon separation can be varied at will. The initial arc acceleration is dependent on the point of contact separation and can thus be varied. It is well known that the interrupting limit of breakers utilizing arc movement depends to a high degree on the initial arc acceleration. Therefore, the ability to vary the point of contact engagement also determines in part the interrupting limit.

It will be noted that contacts constructed in accordance with the present invention incorporate the advantage of multipoint contacts as well as the advantages of rotating arc type contacts. In addition, the slight flexibility and resiliency of the contact rods upon engagement and disengagement of the contacts results in a rubbing action at the various points of contact which keeps the contacting surfaces clean. However, limitations on contact rod flexibility imposed by the contact rod holder insure that the contacts are strong and sturdy. Finally, the contacts are relatively economical and easy to fabricate.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electric circuit interrupter, in combination, a pair of cooperating contacts relatively movable into and out of engagement with each other, at least one contact of said pair of contacts comprising a plurality of electrically conductive rods, each rod comprising a straight shank portion, a first curved portion connected to said shank portion and curved back upon itself in a first plane, and a second curved portion connected to said first curved portion with the second curved portion lying in a plane normal to and intersecting said first plane of said straight shank portion and the first curved portion, each rod in said one contact being adapted to make point contact with the other contact of said pair of contacts when said pair of contacts are in engagement with each other.

2. The combination according to claim 1 wherein said other contact comprises a plurality of rods and wherein each rod in said one contact makes point contact with two adjacent rods in said other contact when said pair of contacts are in engagement with each other.

3. The combination according to claim 1 wherein said other contact comprises a plurality of rods and wherein each rod in said one contact makes point contact with one rod in said other contact when said pair of contacts are in e gagement with each other.

4. In an electric circuit interrupter, in combination, a pair of cooperating contacts relatively movable along an axis into and out of engagement with each other, at least one of said pair of contacts comprising a plurality of electrically conductive rods arranged in regular angular order around said axis, each rod comprising a straight shank portion lying parallel to and spaced from said axis, a first curved portion connected to said shank portion and curved back upon itself in a first plane, and a second curved portion connected to said first curved portion with the second curved portion lying in a plane normal to and intersecting said first plane of said straight shank portion and the first curved portion; each rod in said one contact structure being adapted to make point contact with the other contact of said pair of contacts when said pair of contact structures are in engagement with each other.

5. The combination according to claim 4 wherein said other contact comprises a plurality of rods and wherein each rod in said one contact makes point contact with two adjacent rods in said other contact when said pair of contacts are in engagement with each other.

6. The combination according to claim 5 wherein there are three electrically conductive rods in each contact, and wherein each rod is spaced 120 of angular distance from the adjacent rods in its contact.

7. The combination according to claim 4 wherein said other contact comprises a plurality of rods and wherein each rod in said one contact makes point contact with one rod in said other contact when said pair of contacts are in engagement with each other.

8. In an electric circuit interrupter, in combination, a pair of contact supports relatively movable toward and away from each other, and a pair of cooperating contacts movable into and out of engagement with each other, each of said contacts mounted on one of said contact supports, at least one of said contacts comprising a holder adapted for removable mounting on one of said contact supports and further comprising a plurality of electrically conductive rods mounted in said holder, each rod comprising a straight shank portion, a first curved portion connected to said shank portion and curved back upon itself in a first plane, and a second curved portion connected to said first curved portion with the second curved portion lying in a plane normal to and intersecting said first plane of said straight shank portion and the first curved portion, each rod in said one contact being adapted to make point contact with said other contact when said pair of contacts are in engagement with each other.

9. The combination according to claim 8 wherein each contact comprises at least three electrically conductive rods and wherein each rod in said one contact makes point contact with two adjacent rods in said other contact when said pair of contacts are in engagement with each other.

10. The combination according to claim 8 wherein each contact comprises at least three electrically conductive rods and wherein each rod in said one contact makes point contact with one rod in said other contact when said pair of contacts are in engagement with each other.

No references cited.

ROBERT K. SCHAEFER, Primary Examiner.

ROBERT S. MACON, Examiner. 

1. IN AN ELECTRICAL CIRCUIT INTERRUPTER, IN COMBINATION, A PAIR OF COOPERATING CONTACTS RELATIVELY MOVABLE INTO AND OUT OF ENGAGEMENT WITH EACH OTHER, AT LEAST ONE CONTACT OF SAID PAIR OF CONTACTS COMPRISING A PLURALITY OF ELECTRICALLY CONDUCTIVE RODS, EACH ROD COMPRISING A STRAIGHT SHANK PORTION, A FIRST CURVED PORTION CONNECTED TO SAID SHANK PORTION AND CURVED BACK UPON ITSELF IN A FIRST PLANE, AND A SECOND CURVED PORTION CONNECTED TO SAID FIRST CURVED PORTION WITH THE SECOND CURVED PORTION LYING IN A PLANE NORMAL TO AND INTERSECTING SAID FIRST PLANE OF SAID STRAIGHT SHANK PORTION AND THE FIRST CURVED PORTION, EACH ROD IN SAID ONE CONTACT BEING ADAPTED TO MAKE POINT CONTACT WITH THE OTHER CONTACT OF SAID PAIR OF CONTACTS WHEN SAID PAIR OF CONTACT ARE IN ENGAGEMENT WITH EACH OTHER. 